This is the 12327th most frequent Polish word.
modrzewi
"Modrzewi" means "of larch" or "related to larch (tree)."
The word 'modrzewiowy' here is an adjective derived from 'modrzew', the noun meaning 'larch'. It's used to describe the forest as being composed of larch trees.
Modrzewiowy las otaczał malowniczą dolinę.
The larch forest surrounded the picturesque valley.
In this sentence, 'modrzewiowy' is an adjective modifying 'domku', indicating that the cabin is made of larch wood.
Z domku modrzewiowego dolatywał zapach domowego chleba.
From the larch cabin came the smell of homemade bread.
Here, 'modrzewie' is the plural form of the noun 'modrzew', referring to multiple larch trees.